The present invention relates to an improved method and apparatus for cleaning optical elements in telescopes using a laser beam and, in particular, to such cleaning without illumination or heating of, or damage to the baffles and other structures of the telescope.
Telescopes, operating for example at cryogenic temperatures, are subject to the deposition of such contaminant films as water, carbon dioxide, nitrogen and organic materials on various mirror and other optical surfaces. These contaminant films degrade the performance of the telescope, and techniques involving the use of laser beams have been shown to remove such films, see for example, "Contaminant Removal off Optical Surfaces in Space," L. G. Piper et al, SPIE Vol. 777, 1987, pages 320-332.
Such techniques for removing contaminants utilize relatively large sized, heat dissipating equipment, including laser sources, power supplies, electronics and scan mirrors, all or many of which are placed inside the cryogenic telescope housing. While the large size of such equipment in itself is a disadvantage, primarily as taking up valuable space within the telescope and requiring the telescope to be modified for incorporation of such equipment and possibly obstructing the passage of radiation through the telescope, other more serious problems arise. For example, some portions of certain mirrors may not be covered and cleaned by the laser beam, because limitations as to the number and placement of laser sources do not always allow a direct path to each mirror, and indirect paths by means of reflection from other telescope mirrors may not be along paths for which the mirrors were designed and sized. Further, the cleaning beam and its reflections cannot be fully controlled, and such uncontrolled beam reflections impact onto the telescope structure or its baffles where heating and damage often occurs.